Over the centuries, Americans have answered that question in many different ways. When the United States was young and weak, Washington prudently plotted a path of studied nonintervention, concluding that America’s purpose was to prove that self-government could work at home and “to steer clear of permanent alliances” abroad.

For Jefferson, America’s purpose was “to be a barrier against the returns of ignorance and barbarism” and to build “an empire of liberty.”

For TR, America’s purpose was nothing less than to civilize the world: “The steady aim of this nation,” he declared, “should be to strive to bring ever nearer the day when there shall prevail throughout the world the peace of justice.” When words were insufficient, TR was ready to wield the big stick.

For Wilson, America’s purpose was to make the world “safe for democracy.”

Coolidge said America’s purpose was to spread prosperity, famously concluding, “The chief business of the American people is business.”

FDR outlined America’s purpose during World War II in the Atlantic Charter: to support self-government, promote free trade, defeat Nazism, disarm aggressive nations, ensure freedom of the seas and build a durable system of international security.

Cold War-era presidents followed FDR’s map to define America’s purpose after World War II: to build a network of international institutions aimed at promoting liberal economics and governance, to guard the frontiers of liberty, to deter Soviet aggression. But when the Berlin Wall collapsed and the Soviet Union imploded, the threat that defined America’s place and purpose in the world was gone, and America’s mission statement was in need of revision.

There was a brief moment after 9/11 when there was consensus about America’s purpose in the world, but that consensus evaporated soon after the fall of Baghdad. As President Barack Obama has observed, “Years of debate over Iraq and terrorism have left our unity on national security issues in tatters.”

Regrettably, Obama has not been able to redefine America’s global purpose, let alone rebuild a national consensus in pursuit thereof. This is largely a function of his disinterest in foreign policy and desire to disengage from the world.

What else can be said of a president who repeatedly declares it’s time to “focus on nation-building here at home”; floats phrases like “leading from behind” to defend his worldview; puts an 18-month time limit on pursuing what he himself labeled “our vital national interest” in Afghanistan; admits he doesn’t have a strategy to deal with ISIS; boils U.S. foreign policy down to “Don’t do stupid stuff”; allows sequestration to erode the U.S. military; or insists we are “turning the page on a decade of war,” even as American troops wage war?

In short, there is an air of constraint, even retreat, in the president’s approach to foreign policy and national security. Retired Marine Gen. Jim Mattisdescribesit as a “reactive crouch.”

This shift was predictable, perhaps inevitable. Like a pendulum, U.S. foreign policy was bound to swing back from the hyperactivity of the immediate post-9/11 era. It appears this shift is in line with what a majority of the American people believe. According to Pew polling, 52 percent of the American people say the United States “should mind its own business internationally and let other countries get along the best they can on their own”—up from 30 percent in 2002.

But has the president allowed the pendulum to swing too far in the opposite direction?

With China claiming control over international airspace and waterways, bin Laden’s heirs setting the Middle East and Africa on fire, Russia dismembering and annexing sovereign nations, our European allies begging for help and bracing for invasion, and rogues brazenly detonating nukes (North Korea), building nukes (Iran) and using WMDs (Syria), even the president’s team knows the answer is yes.

Seemingly using the press to send a message to his boss, Secretary of State John Kerry worries, “We cannot allow a hangover from the excessive interventionism of the last decade to lead now to an excess of isolationism.”

Concerned about the toll of sequestration, which was initiated by the Obama administration, outgoing Defense Secretary Chuck Hagel warns, “America must continue to ensure its ability to project power rapidly across oceans…If this capability is eroded or lost, we will see a world far more dangerous and unstable, far more threatening to America and our citizens here at home than we have seen since World War II.”

Former Secretary of State Hillary Clinton bluntly concludes, “Great nations need organizing principles, and ‘Don’t do stupid stuff’ is not an organizing principle.”

Harsh words, but consider the record: When NATO asked for U.S. leadership and equipment in Libya, the Obama administration offered only a “time-limited…military action” and a warning that the extension of U.S. airpower “expires on Monday.” When the president withdrew U.S. forces from a stable Iraq and ignored his own red lines in war-torn Syria, ISIS thrived on the resulting symbiotic chaos. When France asked for help fighting jihadists in Mali, the Obama administration sent Paris an invoice for use of U.S. aircraft. When Kiev asked for weapons to defend itself, Obama sent MREs. When world leaders gathered in defiant solidarity with France after the latest jihadist assault on civilization, America’s president, vice president and secretary of state were absent—a bruising metaphor for America’s reticence and a stark indication that Washington really is more interested in “nation-building here at home” than the burdens of leadership.

The defense that the president is merely reflecting the world-weariness of an inward-looking electorate may be accurate, but that doesn’t make it right. Leadership, especially on matters of national security, is more often than not about setting a direction and a destination—and then convincing the American people to follow. Think about Jefferson abandoning his predecessors’ policies of appeasement and declaring, “It will be more easy to raise ships and men to fight these pirates into reason, than money to bribe them”; Lincoln transforming the Civil War from a struggle to preserve the Union into a struggle to abolish slavery; FDR leading America back onto the world stage; Truman making the case for long-term global containment; Reagan reviving the nation’s flagging commitment to what Truman began; the elder Bush building support for Desert Shield/Desert Storm; the younger Bush building support for the surge.

That’s what leadership looks like in the realm of national security. It doesn’t mean “invading every country that harbors terrorist networks” or “going it alone” or “reacting to the headlines instead of using our heads,” as the president and his army of straw men would argue. What it means is having the resources to deter threats (sequestration is erasing those resources), maintaining hard-earned gains (withdrawing from Iraq gambled away those gains), leading the West (Washington’s stand-off approach to Libya and hands-off approach to Syria were the very opposite), keeping our word (Warsaw and Prague were left out on a limb when Obama reversed course on NATO’s missile-defense plans), and guarding the frontiers of freedom (America’s willingness to do that is very much in doubt in Eastern Europe).

It seems unlikely that the president will have an epiphany the next 23 months and start considering how to strengthen America’s place and purpose in the world. But if he does, a good place to start is with Truman and FDR.

Truman’s example is helpful because he sketched out the blueprint for waging a generational struggle against a determined, transnational enemy. What Truman’s staff wrote in NSC-68 is just as true today: America’s enemies are animated by a “fanatic faith, antithetical to our own.” Now, as then, the challenge is “momentous, involving the fulfillment or destruction not only of this republic, but of civilization itself.” Now, as then, victory depends on recognition that this “is in fact a real war in which the survival of the free world is at stake.”

The president may not like the term “war on terror”; he may want to turn the page on a decade of war; but as Mattis explains, “No war is over until the enemy says it’s over.” ISIS, al Qaeda, AQAP, AQIM, Boko Haram, the Taliban and the rest of bin Laden’s heirs are surging. There are 41 jihadist-terror groups in 24 countries today—up from 21 in 18 countries in 2004. ISIS now numbers 20,000-plus fighters and controls an area the size of Maine. Boko Haram has murdered, maimed and kidnapped its way through Nigeria, carving out an ISIS-style mini-state. The Taliban is circling Afghan’s feeble and increasingly-friendless government.

In short, America must lead and wage this long, twilight struggle against terrorism. Like the Cold War against communism, this will represent much of America’s day-to-day purpose for decades to come. Joint Chiefs Chairman Gen. Martin Dempsey calls it “a 30-year issue.”

FDR’s example is helpful because he understood that America’s peace and prosperity are inextricably linked to the peace and prosperity of the world. He knew that a liberal global order favoring free governments, free markets and free trade would not emerge by accident and would not endure by magic. Now, as in 1941, it depends on America projecting power into the global commons, supporting free government, promoting free trade, defending freedom of the seas and skies and space and cyberspace, and deterring aggressive states. This is America’s enduring purpose.

Capstones is the publication of the Sagamore Institute Center for America's Purpose, where Dowd researches and writes on America's role in the world.